This invention relates generally to test equipment for radio apparatus and more particularly to means for testing radio receivers without the requirement of knowing a priori the frequency to which the receiver is tuned. Present methods of generating modulated RF signals for utilization in receiver testing rely on discrete frequency generation techniques. This requires knowledge of the frequency of the receiver under test and tuning of the RF signal generator is required. Signal generators for testing receivers for various modulation formats, e.g. amplitude modulation, frequency modulation, phase shift key modulation, frequency shift key modulation, and double side band modulation, tend to be rather large and exhibit moderately high power consumption.